On Mon, 01 Jan 2007 18:16:19 +1000, Oliver Fleming wrote:

Hi,
The smaller the diesel engine the harder it has to work to achieve
the
hull speed of the boat.

(Square root of the waterline length X 1.34)

You need the minimum size diesel that will achieve this. If 50
horsepower does it then that is what you need.

The rule of thumb for this is 2hp per ton of displacement. So a 20 ton
boat would need 40hp to reach hull speed, and a 50hp diesel to operate at
80% capacity (another rule of thumb). But this doesn't take wind or waves
into account.

Matt O.